The use of nanoparticulate compounds for modifying properties different from that of the intrinsic nature of paints, varnishes and coatings in general is known and has increased considerably in recent years.
For example, it is known that nanoparticles of metallic silver are used for conferring antibacterial properties on the materials in which they are incorporated, as is shown in the patents cited hereunder.
The use of some metals or their compounds, as agents that help to improve some of the desired properties in products such as coatings, paints and other polymeric mixtures, is common in everyday practice, for example, the use of silver as antibacterial is well known, and it is known that their effect improves substantially when they are of nanometric size. Although materials exist in which nanometric metallic silver is incorporated, said silver is deposited on inert substrates with a size of several microns, resulting in localized zones with a high concentration of nanoparticles.
Zinc oxide is known for its fungicidal effect, and is widely used in personal hygiene articles and skin medications. It is also known that in nanometric sizes it can absorb ultraviolet light, offering protection for materials that contain it. As with all nanometric compounds, better dispersion and controlled particle size offer advantages, since unprotected zones are practically eliminated.
The flame retardant effect of magnesium hydroxide is also known, and it has been observed that in nanometric sizes it offers advantages, for example of transparency, without affecting the mechanical properties of the coating in which it is used. This is embodied in patent application PCT/MX 2007/000046 (Martinez et al., 2007), which relates to a method for the preparation of a flame retardant additive for coatings and the resultant products.
Similarly, the properties of nanoparticles of Ag, Au, Cu, Bi, Mg, Zn, Sb, their oxides, hydroxides, sulfides, chlorides, sulfates, and mixtures thereof, are transferred to the coating of the final application.
Several examples have been found of coatings in which nanoparticles are incorporated to endow them with certain qualities or properties. The main problem to be tackled is the efficient dispersion of the nanoparticles in the application volume, because of the appearance of agglomerates that reduce their effectiveness.
The present invention describes an additive that ensures the homogeneous distribution and efficient dispersion of the nanoparticles throughout the coating. For greater clarity, in this document “additive” means a mixture or combination of components that is added to another substance to give it qualities that it lacks or to improve those that it already possesses. In particular the additive according to the invention is for application in coatings such as paints, varnishes and polymeric mixtures that are fluid at room temperature.
In the prior art there is a great variety of alternatives for incorporating nanoparticles in coatings, and thus provide them with certain properties intrinsic to said nanoparticles, some examples of which are mentioned below.
Patent CN 1850924 (Li, 2006) describes the production of an antibacterial coating containing silver nanoparticles. The additive is prepared using hydroxylated acrylic resin or an emulsion of acrylic acid polymer, starting from a 6% solution of silver nanoparticles in a polyethylene wax. The product obtained in this method cannot be made compatible with other systems and is limited to a maximum concentration of 6%.
Patent CN 1837035 (Wang et al., 2006) gives an account of a method of preparation of a hybrid carbon membrane that contains inorganic nanoparticles. The product of this invention is limited to just one type of application.
Patent JP 2005248136 (Ando, 2005) discusses an additive that contains nanometric silver for coatings, which prevents marine organisms adhering to surfaces. This invention is limited to the removal of marine organisms on surfaces submerged in water and to a paint for marine application.
Patent TW 220398 (Liang, 2004) discusses an additive that contains metallic nanoparticles, but which are synthesized directly in an organic solvent. Application of the product of this invention is limited to materials compatible with organic solvents and that can be synthesized therein.
Patent WO 2003103392 (Norminger et al. 2003) describes a coating that contains antibacterial metallic nanoparticles, but has the limitation that said nanoparticles are on other particles of titanium dioxide.
Publication US20070173564A1 (Sohn et al., 2007) relates to a composition for producing a transparent coating with a photocurable resin, which contains silver nanoparticles. The product of this invention is limited to silver nanoparticles in a photocurable transparent coating.
Publication US2006155033A1 (Sisson, 2006) describes an emulsion used for improving the electrical conductivity between contact surfaces, for example electrical connectors, and for protecting them against the effects of time. This coating is limited to the transfer of electrical properties and to the use of silver nanoparticles.
U.S. Pat. No. 6,855,749B1 (Yadav et al. 2005) is limited to a nanocomposite polymer that is mainly used as a material for biological uses in applications such as vehicles of medicinal products, biomedical devices, and implants of bones or teeth.
U.S. Pat. No. 6,228,904B1 (Yadav et al. 2001) relates specifically to a polymeric composite with nanomaterials with properties of resistivity, the method and the application of the mixture for producing a plastic with electrical properties. The teaching of this document is not directly applicable to fluid mixtures for coatings, as in our case, except that the properties in question are related to the electrical properties.
The additive of the present invention is designed for transferring, to a final coating, biocidal, UV protection, and flame retardant properties, and in general, selected properties intrinsic to the metals and compounds of Ag, Au, Cu, Mg, Zn, Bi, Sb; the additive includes the use of solvents, surfactants, dispersants and resins that make it compatible with the final coating. Said coating with additive ensures perfect distribution and dispersion of the nanoparticles throughout it, without the need for an inorganic substrate. The process for the manufacture of the additive starts from existing nanoparticles of the aforementioned metals and compounds, which can be in aqueous organic media or alternatively as dry powders, and are submitted to a treatment that allows them to be incorporated in coatings used in a wide variety of environmental conditions. The process can be used for obtaining a variety of functionalized additives.